In at least some computed tomograph (CT) imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the "imaging plane". The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a post patient collimator for collimating scattered x-ray beams received at the detector. A scintillator is located adjacent the post patient collimator, and photodiodes are positioned adjacent the scintillator.
Multislice CT systems are used to obtain data for an increased number of slices during a scan. Known multislice systems typically include detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of detector elements form separate channels arranged in columns and rows. Each row of detectors forms a separate slice. For example, a two slice detector has two rows of detector elements, and a four slice detector has four rows of detector elements. During a multislice scan, multiple rows of detector cells are simultaneously impinged by the x-ray beam, and therefore data for several slices is obtained.
A multislice CT system requires source collimation to flood the detector with a uniform x-ray beam intensity in the z-axis. This is necessary to avoid image artifacts that would otherwise be caused by the normal movement of a non-uniform x-ray beam over a non-uniform z-axis detector response. Unfortunately, much of the x-ray beam typically falls unused off the ends of the detector resulting in low dose efficiency and a high patient dose.
Accordingly, it would be desirable to provide a CT system that utilizes all of the x-ray beam which allows selection of the number and thickness of the scan slices to reduce patient x-ray dosage and improve x-ray beam efficiency.